(Damjanovski) Lecture 5

Question 1

Structure of microtubules

Answer 1

alpha and beta subunits

Question 2

How big are the alpha and beta subunits in microtubules?

Answer 2

55 kilodaltons

Question 3

Dimensions of microtubules

Answer 3

Hollow tubes
* 25 nm in diameter
* 100s of micrometers long

Question 4

What is the difference of alpha to beta tubulin?

Answer 4

Alpha tubulin cannot hydrolyze GTP (always GTP)
Beta tubulin can hydrolyze GTP (GTP to GDP)

Question 5

When does GTP hydrolization occur in microtubules?

Answer 5

During microtubule growth/polymerization

Question 6

Singlet microtubule

Answer 6

13 protofilaments

Question 7

Doublet microtubule

Answer 7

13 protofilament tube + 10 protofilament tube

Question 8

Triplet microtubule

Answer 8

13 protofilament tube + 10 protofilament + 10 protofilament

Question 9

How does lettering for the microtubules?

Answer 9

A for the 13 protofilament
B and C for each additional 10 protofilaments

Question 10

MTOC

Answer 10

Microtubule Organizing centers

Question 11

What are examples of MTOCs?

Answer 11

1. Centrosome
2. Spindle Poles
3. Basal Body

Question 12

Which end is in MTOC?

Answer 12

Always the (-) end

Question 13

What is the only exception to the (-) end in the MTOC rule?

Answer 13

Dendrites

Question 14

Centrosomes contain…

Answer 14

Centrioles

Question 15

Do plants have centrosomes?

Answer 15

No, they do not have centrioles

Question 16

What angles are centrioles to each other?

Answer 16

Perpendicular

Question 17

What surrounds the centrioles?

Answer 17

Pericentriolar matrix

Question 18

What is the structure of a centriole?

Answer 18

9 triplet microtubules

Question 19

What is the purpose of pericentriolar matrix?

Answer 19

For replicating chromosomes

Question 20

What provides nucleating sites for microtubules in the periocentriolar matrix?

Answer 20

Gamma-tubulin ring complex (gammaTuRC)

Question 21

What facilitates microtubule branching with gammaTuRC?

Answer 21

Augmin

Question 22

What is the purpose of a nucleation site?

Answer 22

Accelerates initial polymerization

Question 23

What does the term “catastrophe” imply?

Answer 23

Depolymerization

Question 24

What is dynamic instability?

Answer 24

The constant polymerization and depolymerization (growing and shrinking) of cytoskeletal components

Question 25

What is the purpose of dynamic instability?

Answer 25

Allows cells to transport etc.

Question 26

What does dynamic instability of microtubules depend on?

Answer 26

Presence/absence of a GTP-beta-tubulin cap

Question 27

What does a GTP cap do in microfilaments?

Answer 27

Allows GDP protofilaments in the center to be stable (they will depolymerize without the cap)

Question 28

With the GTP-beta tubulin cap, what is the (+) end described as?

Answer 28

Smooth

Question 29

What happens to the smooth ends during depolymerization?

Answer 29

Fray * Allows depolymerization to continue towards the (-) end

Question 30

When will fraying/weakening of cohesion between protofilaments occur?

Answer 30

When GTP to GDP hydrolysis reaches the (+) end

Question 31

What drugs depolymerize microtubules?

Answer 31

Colchicine

Question 32

What drug stabilizes microtubules?

Answer 32

Taxol

Question 33

MAPs

Answer 33

Microtubule Associated Proteins

Question 34

What do MAPs do?

Answer 34

* Alter microtubule stability * Bundle microtubules

Question 35

How are MAPs regulated?

Answer 35

Phosphorylation * Phosphorylation promotes disassembly (e.g. CDK in cell cycle)

Question 36

Some MAPs contain MT binding domain and "projection" domain, what can this help with?

Answer 36

Can regulate microtubule spacing

Question 37

What are components in the structure of MAPs?

Answer 37

* Binding domain * Projection domain

Question 38

What are the 2 MAPs that we talked about? How are they different?

Answer 38

MAP2 - Longer projection domain Tau - Shorter projection domain

Question 39

What do the binding domain in MAP2 and Tau do?

Answer 39

Acts as a coat, prevents depolymerization

Question 40

What are special MAPs that associate with the (+) ends of MTs called?

Answer 40

+TIPs

Question 41

What is one +TIP that we talked about?

Answer 41

EB1

Question 42

What does EB1 do?

Answer 42

Moves to the (+) end * Possibly has roles in stabilization and promoting polymerization/reducing catastrophe

Question 43

What proteins can stabilize growing protofilaments and/or prevent catastrophe?

Answer 43

XMAP215 CLASP

Question 44

What do XMAP215 and CLASP proteins contain that stabilize the profilaments?

Answer 44

TOG domains

Question 45

What removes terminal dimers that requires ATP hydrolysis?

Answer 45

Kinesin-13

Question 46

What binds to the ends of protofilaments and may promote GTP hydrolysis (promote fraying)?

Answer 46

Stathmin

Question 47

What inactivates Stathmin?

Answer 47

Phosphorylation

Question 48

Microtubule types in basal body

Answer 48

Triplet microtubules

Question 49

What happens in the transitional zone in basal bodies and cilia/flagella?

Answer 49

The triplet microtubules become doublet microtubles * The singlet microtubules in the middle are not present

Question 50

How are basal bodies different from centrioles?

Answer 50

Basal bodies polymerize tubules directly (doesn't require periocentriolar matrix)

Question 51

What is axonmeal bending powered by?

Answer 51

Axonemal dynein * IMPORTANT: REMEMBER THE AXONEMAL PORTION

Question 52

What is critical for axoneme bending?

Answer 52

Nexin

Question 53

What happens is nexin is not present in the basal body?

Answer 53

The two microtubules will slide past each other